ios and apple music desktop not syncing play count (but music playlists sync fine!)

I've had this issue forever. I've been too annoyed to bother addressing it, so I don't believe it has to do with updating any software.

Regardless, I have automatic updates enabled on all devices (always).

I have followed the advice on older support posts regarding this issue. So, both media and home sharing are enabled (Settings > General > Sharing > Media Sharing).

BUT, the playlists and songs do sync!

So, obviously, I'm signed into the same account.

I do ALL the downloading/updating to the library via the desktop app.

What now?